Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to methods and apparatus for improving the overall decision quality of the F-DPCH channel based on the channel conditions of a base station, thereby providing consistent service in a wireless communication system.
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
In a typical wireless communication environment, RF signal transmissions between a base station (e.g., NodeB in UMTS) and user equipment (UE) are subject to degradation, such as path loss, shadow fading and multipath, which typically caused by such factors as terrain contours (e.g., mountains, forests), environment (e.g., urban or rural), propagation medium (dry or moist air), changes in distance between a base stations and a mobile UE, etc. A transmit power of the UE is typically controlled by downlink (DL) Transmit Power Control (TPC) commands that are sent from the NodeB to the UE through a downlink (DL) channel. The UE decodes these DLTPC bits (e.g., where a “0” represents a “down” or reduce power command, and a “1” represents and “up” or increase transmit power command) and adjusts the transmit power accordingly. DLTPC can be carried in either a regular Dedicated Physical Channel (DPCH), or a Fractional-DPCH (F-DPCH) channel which constitutes only DL TPC symbols.
When the F-DPCH channel is used, downlink power control may be adopted on the serving base station F-DPCH to warrant a desired level of decoding performance of the DL TPC bits of the base station. The UE may request a change in downlink transmission power by sending uplink (UL) TPC commands on an uplink to the serving base station. The transmission of ULTPCs on the uplink to the base station and the receiving of DLTPCs on the downlink from the base station may be referred to as a power control loop.
In an aspect where the UE has a power-controlled channel from a serving base station but is experiencing bad channel conditions, the F-DPCH power control may not work properly to warrant a desired level of DLTPC decoding performance. In other words, in bad channel conditions such as severe path loss and/or fading, the serving base station may not be able to transmit the F-DPCH channel (and consequently the DLTPC bits) with a power required for reliable reception by the UE, as the base station may already be transmitting at a maximum DL power or the base station could not hear UE's DL power request due to a bad uplink. In these cases, the channel decoding performance at the UE may not be maintained at a desired level, and the decoding error rate may be very high. This results in bad DL power control and difficulties to retain UL/DL connections.
In another aspect, since non-serving base station F-DPCH channels are not power controlled, their DL TPC decoding performance is not protected from channel variations. As such, in bad channel conditions, this may lead to large amount of DLTPC decoding errors for non-serving base stations DLTPC, and thus an inaccurate decision after combining with serving base station DL TPC. Again, this results in bad DL power control and difficulties to retain UL/DL connections.
Thus, aspects of this apparatus and method for to improving the overall decision quality of the F-DPCH channel based on the channel conditions of a serving base station and a non-serving base station.